Rovibrational cooling of molecules by optical pumping Experimental - - PowerPoint PPT Presentation

Rovibrational cooling of molecules by

• ptical pumping

Experimental results for laser cooling of molecules

Isam Manai isam.manai@u-psud.fr

Laboratoire Aimé Cotton Orsay France

Quantum Technologie Conference III Septembre 9-15, 2012

Cold Molecules: Why?

1012 109 106 n/cm3 T/K 10-9 10-6 10-3 1

Precision measurement Fundamental test

small velocity nK µK mK K lDB = h/mv ∝ T-1/2 (quantum size)

~

classical size of particles (1nm)

Control of collisions Quantum chemistry

lDB ~ distance between particles

Quantum properties Bose-Einstein gaz Quantum information

Precise/long measurement

• Cold molecules  Slow molecules  long interaction time Dt

OH, CO, … radiative lifetime (50ms) PRL 95 013003 (2005)

• DE ~h/Dt  precise measurement (atomic clock)

ND3 hyperfine structure (Hz) EPJD 31 337349 (2004)

• G. Meijer (Berlin) , J. Ye (JILA), …

Effect of black body radiation!

Fundamental test

Variation of constant (103 better than atoms): PRL 99, 150801 (2007) * OH electronic level PRL 96 143004 (2006).

Compare fine-structure with astrophysical data Da/a < 10 -16 /year

* Variation of me/mp or constant α in spectra.

Conincidence vibration and fine structure levels

* Electron dipole (d) moment YbF (Hinds), PbO (DeMille, Doyle),...

Shift –d.E due to electric E field inside the molecule GV/cm

• Chirality: BaF or HSiO D. DeMille et al. PRL 100, 023003 (2008)

Improved measurement of the shape of the electron: Nature 473, 493 (26 May 2011)

Control of (Reactive) collisions: quantum chemistry

• J. Ye, G. Meijer, G. Rempe, J. Doyle, M. Köln, H. Lewandowski …
• macromolécules (perfluorinated) M. Arndt
• Ions : M. Drewsen, S. Schiller, R.Wester, …
• Reactions at zero temperature (Resonnance, Tunneling)
• Collisions in fields. External field to control dynamic
• Create cold atoms by photodissociation SO2  SO + O EPJD 46, 463 (2008)
• CH3F + Ca+  CaF+ + CH3
• T. Sofltey PRL 100, 043203 (2008)

1)Photoassociation and cold molecules 2)Rovibrational Cooling of Cesium molecules by Optical pumping 3) Conclusion

Outline

R (1) 6s+6p3/2

1/R3 1/R6

kBT 25 50 75 100 125 Energy 6s1/2+6s1/2 Internuclear distance

Photoassociation

(2'') Photoassociation

Absorption of one photon by two cold atoms (T~100mK)

(1)

Desexcitation

(2'') (2') Cold molecules Hot atoms

Molecules in several vibrational levels

(2')

PA laser Detection laser

Experimental Setup

• PA: Ti:Sa continu, 852 nm, ~1W
• Detection (ionization): pulsed laser

10 Hz-7ns, 5-10mJ/pulse

• Optical pumping: femtoseconde laser,

12.5 ns, 770 nm, 1W

Cs - MOT ~ 5 .107 atoms ~1011at/cm3 ~100µK

15900 15920 15940 15960 15980 16000 10 20 30 40 50 60 70 80 90

Cs+ 2

Fréquence de détection (cm

• 1)

5 10 15 20 25 30

• 5000

5000 10000 15000 20000 25000 30000

VX

Laser d'ionisation PA

Cs+ 2 Cu

X+

g

6s+

Energie (cm-1)

R (a0) Bu

• Em. Spon

PA

t (ms)

20 40 49 50

Détection

Population after Photoassociation

vX = 0vC = 1 vX = 0vC = 0

Need: Vibrational cooling Optical Pumping using shaped broadband laser

Science 321, 232 (2008)

12800 12900 13000 13100 20 40 60 80 100 120 140

Intensité nombre d'onde (cm

• 1)

8 9 10

R (A0)

v=0

1 2 3 i

8 9 10

• 3600
• 3500
• 3400
• 3300
• 3200

9200 9300 9400 9500 9600 B

1u

Energy (cm

• 1)

R (A0)

X

1 + g

8 9 10

R (A0)

v=0

8 9 10

R (A0)

v=0

15900 15920 15940 15960 15980 16000 10 20 30 40 50 60 70 80 90

Cs+ 2

Fréquence de détection (cm

• 1)

15900 15920 15940 15960 15980 16000 10 20 30 40 50 60 70 80 90

vX-vC = 0-0 0-1 0-2

• Optical pumping

Femto

5 10 15 20 25 30

• 5000

5000 10000 15000 20000 25000 30000

VX

Laser d'ionisation PA

Cs+ 2 Cu

X+

g

6s+

Energie (cm-1)

R (a0) Bu

• Em. Spon

PA

• pt. pump

t (ms)

20 40 49 50

Detection

Population after pumping

Efficiency ~ 65 %

12750 12900 13050 13200 0.0 0.4 0.8

Intensity (Arb) Wavenumber (cm-1)

Experiment

0.0 0.4 0.8

Simulation

Pumping to the dark v=1

Intensity (Arb)

Energy

Internuclear distance

V=1 dark Other v coupled X X X NJP 11 055037 (2009)

Better amplitude shaping

Collaboration with Béatrice Chatel, Laboratoire Collision Agrégat Réactivité, Toulouse

Liquid Crystal spatial light modulator (SLM) 640 pixel 0.06nm resolution ~ 1 cm-1

12600 12800 13000 13200 0.0 0.4 0.8 0-0 0-1 15920 15960 16000 10 20 30 40

Cs2

+

Pumping to a chosen dark state !

V=0 dark

Intensity (Arb) Cs2

+ 1-0 1-1 1-2 1-3 15920 15960 16000 10 20 30 40

12600 12800 13000 13200 0.0 0.4 0.8

V=1

12600 12800 13000 13200 0.0 0.4 0.8 2-1 2-2 2-3 2-4 15920 15960 16000 10 20 30 40

Cs2

+

Intensity (Arb)

V=2

12600 12800 13000 13200 0.0 0.4 0.8

Wavenumber (cm-1) Wavenumber (cm-1)

7-8 7-9 7-10 7-11 15920 15960 16000 20 40 60

Intensity (Arb) Cs2+

V=7 Efficiency ~ 60% with SLM 3%

• ff/on

ratio b) c)

a)

Intensity (Arb)

d)

Energy

Internuclear distance

V=2 dark Other v coupled X X X NJP 11 055037 (2009)

15900 15920 15940 15960 15980 16000 10 20 30 40 50 60 70 80 90

Cs+ 2

Fréquence de détection (cm

• 1)

15900 15920 15940 15960 15980 16000 10 20 30 40 50 60 70 80 90

vX-vC = 0-0 0-1 0-2

• Optical pumping

Femto

5 10 15 20 25 30

• 5000

5000 10000 15000 20000 25000 30000

VX

Laser d'ionisation PA

Cs+ 2 Cu

X+

g

6s+

Energie (cm-1)

R (a0) Bu

• Em. Spon

PA

• pt. pump

t (ms)

20 40 49 50

Detection

Population after pumping

Efficiency ~ 65 %

In one vibrational level many rotational levels are populated

Detection of the rotation

vX=1

JX= 3 2 1

vX=0 vC=1

JC= 4

3 2 1 vC=0 C

1u

X

1 + g

• Detection:
• For one vibrational level many rotational levels

are populated

• Rotational separation (~600MHz)

Unresolved with the REMPI detection (3 GHz)

JB= 4 3 2 1

vB=3 Diode de détection vX=7

JX= 4 3 2 1

vX=0

20 16 12 8

Cs2

+ Number 13142.00 13141.95 13141.90 13141.85 13141.80 13141.75

Wavenumber [cm

• 1]

P(4) P(2) Q(4) Q(2) R(2) R(4) R(0)

REMPI detection in vX = 7 Detection with a narrowband laser Desexcitation to many vibrational levels

• Detection:
• For one vibrational level many rotational levels

are populated

• Rotational separation (~600MHz)

Unresolved with the REMPI detection (3 GHz)

Detection of the rotation

Pulsed laser

20 16 12 8

Cs2

+ Number 13142.00 13141.95 13141.90 13141.85 13141.80 13141.75

Wavenumber [cm-1]

P(4) P(2) Q(4) Q(2) R(2) R(4) R(0)

Selection rules : ΔJ = 0, ±1 +  -

–P : J decrease by 1 in absorption –Q : J constant –R : J increase by 1 in absorption

2) Rotational cooling a modifies the vibration  vib. cooling needed In practice: Cs2 rotational structure too small to be shaped with grating Too cool the rotation we use excite the P branch Only Even rotational distribution are populated The rotational states have a (+/-) parity given by the sign of (-1)J’+1 in 0g

• and (-1)J in 1X∑g

Selection rules : ΔJ = 0, ±1 +  -

–P : J decrease by 1 in absorption –Q : J constant –R : J increase by 1 in absorption

Rotational cooling

V= 0 , J = 0

16 14 12 10 8

nbre d'ions

13.14200x103 13.14195 13.14190 13.14185 13.14180

fréquences [cm-1]

R(3) R(1) Q(1) Q(3) Q(5) P(3) P(5)

20 16 12 8

Cs2

+ Number 13142.00 13141.95 13141.90 13141.85 13141.80 13141.75

Wavenumber [cm-1]

P(4) P(2) Q(4) Q(2) R(2) R(4) R(0)

The green spectrum : only odd rotational levels are populated The black one : only even rotational levels are populated The rotational states have a (+/-) parity given by the sign of (-1)J’+1 in 0g

• and (-1)J in 1X∑g

V= 0 , J = 1 V= 0 , J = 4

Conclusion

• Accumulation of molecules in a choosen vibrational level using a shaped

broadband femtoseconde laser

New Journal of Physics, 11(5)(2009) Journal of Modern Optics, 56:2089-2099,(2009). Molecular Physics, 108 :795{810, (2010)

Our vibrational cooling method is genaral method and can be used in any molecules, demonstrated recently in Bigelow group for NaCs molecules

Optics Express, Vol. 20, No. 14, (2012)

Conclusion

• Rovibrational cooling of Cs2 molecules are also demonstrate

Accepted in PRL Transfert of molecules in a choosen rotational level

V= 0 , J = 0 V= 0 , J = 4 V= 0 , J = 1

Perspectives

* With rovibrational cooling collision between molecules and atoms can be studied. * The method of rovibrational cooling could be extended to other molecules

and molecular beams.

* And also opens up general perspectives in laser cooling the external degrees of

freedom of molecules.

Visitors

 Marin Pichler  Maria Allegrini  Goran Pichler  Emiliya Dimova  Lirong Wang

Theory LAC

 Nadia Bouloufa  Olivier Dulieu

Experiment LAC

 Isam Manai  Ridha Horchani  Mehdi Hamamda  Daniel Comparat  Hans Lignier  Pierre Pillet

Collaboration

 Béatrice Chatel  Sébastien Weber

(LCAM, Toulouse, France)

Thank you for your attention !